Tandem-operated echo suppressor



July 14, 1925.

INVENTOR J13.- M Wfit Airmen/51 S. B.- WRIGHT TANDEM OPERATED ECHOSUPPRESSOR Flled July 2 1924 I mi .4,

Patented July 14, 1925.

. SUMNER B. WRIGHT, OF EAST f 1,545,541 ur OFFICE."

ORANGE, NEW" JERSEY, ASSIGNOR TO AMERICAN TELE- PHQNE AND TELEGRAPHCOMPANY. A CORPORATION OF NEW YORK.

TANDEM-OPERATED new; i

Application filed July 2,

'1'0 all "whom it may concern:

rcsiding at East Orange, in the county of Essex and State of New Jersey,have invented certain Improvements in- '.l:nidem-()perated EchoSuppressors, of which tlie tollowing is a specification.

This invention relates to transmission 'circuits, and more particularlyto transmission circuits employing echo suppressors.

One of the objects of the invention is to provide an arrangement wherebytwo or more circuits, each equipped with echo sup pressors, may beoperated intandem. The problem presented when two or more circuits, eachhaving an echo suppressor, are switched together, is to prevent the circuits getting into such a condition that, when two subscribers at theends begin to talk at about the same timc,.neithcr subscriber will beable to hear the other. i

The nature ol. the trouble will be evident if we imagine the twocircuits, each containing an echo.suppressor, are connectial togethcr.It the subscriber at end A bcgins to talk, the voice currents generatedwill cause the suppressor near his end to operate in such a wayas toshort-circuit the transmission path coming from the subscribcr at theend B. If, before the voice currents from the subscriber at end A reachthe second suppressor near the end it, the subscriber at end B hasalready started to talk and the voice currents generated at his stationhave caused the suppressor near his end to operate, it will be evidentthat the voice of the subscriber atA will be blocked by the the voice ofthe subscriber at 15 will be blocked by the suppressor'near the A cnd.Talking under these conditions would be dillicult because part or" thetime both subscribers might be talking with neither one hearing theother. I

.In accordance with the present invention it is proposed to overcomethis dilliculty by a ranging two transmission circuits adapted tandem insuch a manner Be it known that I, SUMNER BiHnunrr,

to be connected in that when a tandem connection is established. theecho suppressor uiiitffor shorten-coil ing the path transmitting westwill be disablcd in the case of the one circuit. and the echo suppressorunit for short-circuiJ ing the path transmitting east will be disabledin thc rasc of the other transmission circuit. Under 'oll' transmissionsuppressor near end it while 7 SUPPRESSOR.

1924. Serial No. 723,802.

one echo suppressor for transmission in a it will not be possible Iprovided with echo suppressors of the ordinary type and arranged to beconnected in tandem, while Fig. 2 illustrates'a similar pair oftour-wire repeater circuitsprovided with means for disabling certailrofthe echo suppressor units in accordance with the present in vention; 4

Referring to Fig. 1, a four-wire circuit is schematically shown, saidcircuit being equipped with the usual one-way repeaters and an echo suipress'or-between stations A and l5, while a similar circuit is shownbetween stations l3 and G. ncctiims'over either circuit, each individualecho suppressor tunctions in its normal man nor, that. is, whentransmission takes place from. A to B the A--l3 suppressor operates andslmrt-cirmaits the opposite branch of the tour-wire circuit, suppressingechoes from I5, and vice versa. If these two circuits gcthcr in tandemand a person at A began talking to a person at l, the A-li supprcssorwould operate and cut olt transmission .lrom C, while a short time laterthe l-----(. supprcssor would also o}.)crate*and cut from (3. ll",however, during the interval between the operation of the A-l5 and l-Csuppressors, waves from the party at C should arrive .at the suppressorC-l3, these waves would operate the GB suppressor, thus cutting'o'tt'transmission from Fnrthern orc, since the AB suppressor wouldalreac'ty'be operated, the transmission l'rom the subscriber at C couldnot get through to A aiul p artics at both A and (i might talk for sometime without either hearing the other. A Fig. 2 shows. schematically. anarrangement for obviating this dilliculty by making one-half of eachsup'prcssor inoperative wbcn tlre'two circuits are coniuwted together inlandcm. In this ligurc, an operators through tollcortl circuit is shownat ll betwccn the two l'iiuravirc circuits. This toll-I cord isarrangcd'so that when all four of its vFor terminal conill) plugs areinserted in the line and network 13Cks by which the four-wire circuitsare terminated at station B, the line terminals of the four-wire.circuits as Well as the network terminals will be directly connectedtogether. By means of this connection it will be apparent that an almostperfect condition of balance will obtain at each hybrid coil by reasonof the fact that the circuit connected to the line jack is identicalelectrically with the circuit connected to the network jack. In short,there is practically no unbalance at the B terminalsof either four-wirecircuit, so that the effect is practically the same as though theindividual lines of the two four-wire circuits were directly connectedtogether at station B.

\Vhen the toll cord establishes the connection between the two four-wirecircuits in tandem, a ground is connected to thesleeve conductor of theline jack of the four-wire circuit extending from station A to stationB, thereby causing current to flow through .a control wire (which may bea simplex or composite circuit of any well-known type, if desired) tooperate a relay X atthe fourwire repeater station at which the echosuppressor A-B is applied. This relay renders the AB half 'of the echosuppressor inoperative by opening the shortcircuit controlled by the ABhalf of the sup-- pressor, the B-A half of the suppressor, however,remaining in its normal condition.

7 Similarly, the C-B half of the echo suppressor on the circuit betweenB and C is rendered inoperative when the other end of I l the toll cordis inserted in the line jack at B by means of a ground applied toanother similar control wire to operate the relay Y. The B-C half of thesuppressor is not disabled, however, as the relay W remains normalbecause the sleeve at C j is not grounded.

The resulting effect is, therefore, that of a four-wire circuit equippedwith a single 'eeliosuppressor arrangement, the two halves of which arelocated not near the center of the circuit but one near the receiving enfor each direction. Consequently, when the subscriber at'A talks to thesubscriber at C, the voice currents will ,be transmitted through stationover the upper lines of wire ciicii mils west,

each four-wire circuit, and upon arriving at the point where the echosuppressor B-C is applied, ..the latter suppressor. will be opcrated'to'short-circuit the line of the fourit between B. and C which trans- Thisprevents C to A so that echo currents transmitted through the, hybridcoil at C cannot be propagated back to station Theline trainsn'i'itiingw cstbelwccn stations A and B is, of cm'u'se, not disabled so thatanyrclm currents which pass through the hybrid coil of the four-wirecircuit bet een A and B at station ever, may

transmission fromrents transmitted in.

B will be transmitted back to the subscriber at A. As already pointedout, however, the balance at this. point will be almost perfect as itdoes not depend upon the simulation of a real line by a network.Therefore, the echo currents which will be returned'to station A fromthis point'will be so small in volume that they may be disregarded. Theecho currents transmitted through the hybrid coil at station C, howhaveconsiderable magnitude because the balance at that point depends up onthe simulation of a real line bya compromise network so that theunbalance may be considerable. Echoes transmitted to A from this point.are prevented, however, by means of the echo suppressor unit B-O.

The method above described is applicable to circuits built up of morethan two fourwire repeater circuits equipped with individual echosuppressors. For example, it will be apparent that if a connection be Cto a third four-wire circuit established at by means of a toll cordconnection similar to that shown at -B,.the relay W would be operated todisable the suppressor unit'B C and its place would be taken by half ofanother suppressor located at a point beyond Similarly, if a connectionis established at A to another four-wire circuit, the relay Z *"ill beoperated to disable the suppressor nit BA, its place in turn being takenby one-half of a suppressor unit located beyond A. It will beunderstood, of course, that where connections are to be. established ateither A or O to other four-wire circuits, the network N .will bedisconnected and connections established to network jacks, as shown atstation B. It will be obvious that the general principles hereindisclosed may be embodied in many other organizations widely difi'erentfrom those illustrated without departing from the spirit oftheinventionas defined in the following claims.

What is claimed is:

i1. In a transmission system, a plurality of transmission circuitsadapted to be connect ed in tandem, a pair of echo suppressor unitsassociated with each circuit, one being responsive tocurrentstransmitted in one direction for disablingthecircuit fortransmission in the opposite direction, being responsive to currentstransmitted in the opposite direction for disabling thecircuit fortransmission in the'first direction, and means operating upon theconnection of said circuits in tandem to render all of said echosuppressor units ineffective except-one pair, of which one will beresponsive to ourother responsive to currentstransmitted in the oppositedirection.

2. In a transmission one direction and the system, a plurality oftransmission circuits adapted tobe connectlllll the other V I sponsiveto currents transmitted in one direction-Ior disabling the circuit fortransmission in theopposite direction, the other being responsive tocurrents transmitted in the opposite direction for disabling the circuitfor transmission in the first direction,

means for connectin said transmission circults-1n tandem, an circuitscontrolled by said means for rendering all of said echo suppressor unitsineffective except one pair,

of which one unit will be responsive to ourrents transmitted in onedirection and the other unit will be responsive to. "currentstransmitted 'in the opposite direction.

3. In a transmission system, a plurality of transmission circuitsadapted to be connected in tandem, a'pairof echo suppressor unitsassociated with each circuit, one being re sponsive to currentstransmitted in one direction for disabling the circuit-for transmissionin the opposite direction, the other being responsive to currentstransmitted in the opposite direction for disabling the circuit fortransmission in the first direction,

and means operative when said circuits are connected 111 tandem torender all of said echo suppressor'units inefiective except one unitassociated with one of said circuits and res 'onsi've to transmission 1none direction an I another unit associated with another of said circuitsand responsive to currents transmitted in the opposite direction.

4. In a transmission system, a plurality of transmission circuitsadapted to be connected in tandem a pair of echo suppressor unitsassociated wlth each circuit, one being responsive to currentstransmitted in one direction for disabling the circuit for transmissionin the opposite direction, the other being responsive to currentstransmitted in the opposite direction for disabling the circuit fortransmission in the first direction, means to connect said transmissioncircuits in tandem, and circuits controlled by said with one of saidtransmission circuits and responsive to currents transmitted in onedirection and another unit associated with another of said transmissioncircuits and responsive to currents transmitted in theoppositedirection.

In testimony whereof, I have signed my name to, this specification this1st day, of

July, 192%.

, SUMNER B. WRIGHT.

